1. Field of the Invention
The present invention relates to an apparatus and method for optical disc drive operations, and more particularly, to a disc type determining apparatus and method in which vibrations generated in a drive by a disc are measured, and then, using the measured vibrations, determining whether the disc is a deflected disc, an eccentric disc, or a mass eccentric disc, and based on this determination, setting the transfer rate of the determined disc.
2. Description of the Related Art
Discs having a deflection, an eccentricity, and a mass eccentricity larger than those of a normal disc are referred to as a deflection disc, an eccentricity disc, and a mass eccentricity disc, respectively. In these special discs, disturbances occur caused by vibrations not damped by a servo in a focus and tracking control loop. Therefore, in a disc drive, it should be determined whether a received disc is a special disc. If the results indicate that the disc is a special disc, the transfer rate of the disc should be limited such that a normal drive operation is performed according to the deflection, eccentricity, and mass eccentricity.
If the deflection, eccentricity, and mass eccentricity of the disc increase, disturbances increase for which a focus and tracking control loop should compensate. Moreover, if the transfer rate of the disc increases, the rate of change of the disturbances increases and all servo operations become unstable. In particular, after a search or a layer jump operation, a focus and tracking control cannot start in a stable mode. Therefore, only when the speed of a spindle motor is limited to a predetermined value at which a normal servo operation is performed in accordance with the deflection, eccentricity, and mass eccentricity of the special disc can data be stably recorded on and reproduced from the special disc.
In order to limit the speed, an algorithm is used to determine whether a received disc is either a deflection disc, an eccentric disc, or a mass eccentric disc. However, according to algorithms used conventionally, the result of the determination varies according to a state of the servo. Also, since there is no algorithm appropriate to determine if the special disc is the disc deflection, there are many disc drive models which do not determine or recognize whether the disc is a deflection disc.
FIG. 1A shows a focus error signal used in measuring the deflection of a disc. The amplitude of this focus error signal is then used as data to determine whether the disc is the deflection disc. FIGS. 1B and 1C are, respectively, a waveform diagram of a tracking error signal used to generate a tracking zero cross (TZC) used in measuring disc eccentricity, and a TZC signal generating block. The tracking error signal of FIG. 1B is compared with a reference value in a comparison unit 10 of the TZC signal generating block of FIG. 1C. The result of the comparison is compensated in a compensation unit 11 so as to generate the TZC signal. Since the TZC signal is output as a sequence of pulses whenever a pickup (not shown) passes through one track, the number of this TZC pulses is calculated and used as data for determining whether the disc is the deflection disc.
Conventionally, determining whether a disc is the deflection disc, the eccentric disc, or the mass eccentric disc is performed in an initial lead-in operation. A microcomputer (not shown) normally drives a drive with automatic adjustment, and then determines the disc type by the following methods.
Deflection Disc:
For a constant focus control loop gain, a disc having a great deflection has a great focus disturbance, a deflection component which is not controlled is great, and the amplitude of the sine wave appearing in the focus error signal of FIG. 1A increases. Therefore, by measuring the amplitude of the focus error, it can be determined if the disc has a large deflection.
In order to increase the measuring resolution, the focus loop gain is reduced and the output of the focus error signal is increased.
In the prior art, the focus error signal is read by a microcomputer (not shown). If the obtained amplitude of the signal is greater than a predetermined value, it is determined that the received disc is the deflection disc. The greater the amplitude of the focus error signal, the greater deflection of the received disc, and therefore the maximum transfer rate of the disc is reduced. However, if the focus error signal is used to determine the disc deflection, the measuring reliability is degraded because the signal is greatly affected by noise. Therefore, in most disc drive models, this method is not used. Even when this method is used, the importance of the determining the disc deflection is minimized.
Eccentric Disc:
In a state where only focus control is performed, a track transverse signal as shown in FIG. 1B is a tracking error. Since the number of sine waves output during one disc rotation cycle varies with respect to the eccentricity of the disc, the eccentricity of the disc can be calculated by counting the number of pulses of the sine waves output during one disc rotation cycle. For this, the TZC signal, used to find the number of tracks passed in searching, is employed.
The eccentricity of the disc is obtained by multiplying the number of pulses of the sine wave output during one disc rotation cycle by (track pitch/2). Using the calculated eccentricity, it is determined whether the disc is the eccentric disc, and the speed of a spindle motor is limited according to the eccentricity. The prior art method for measuring disc eccentricity is widely used for many drives because it is more reliable than the method for measuring disc deflection.
Mass Eccentric Disc:
The mass eccentric disc presents a small eccentricity for a low transfer rate, but the eccentricity increases for a high transfer rate. Accordingly, when an algorithm for measuring disc eccentricity is used, if the number of pulses of the sine wave output during one disc rotation cycle at the low transfer rate is almost the same as that at the high transfer rate, the received disc is not the mass eccentric disc. If the difference in the number of pulses is great, the received disc is a mass eccentric disc. Here, according to the difference of the number of pulses, the maximum transfer rate is limited.
As described above, in the prior art, the disc deflection, the disc eccentricity, and the disc mass eccentricity are not directly measured. Instead, an algorithm is used which utilizes general characteristics. For instance, the general characteristics include that if the deflection, the eccentricity, and the mass eccentricity increase, the amplitude of the focus error increases, or the number of pulses of the sine waves increases during the output of a disc rotation frequency. The eccentricity algorithm has a relatively high accuracy and is used in most disc drive models, while the deflection algorithm has a low accuracy and a high probability of erroneous determination, and is rarely used. If the type of the special disc is not distinguished and the transfer rate is not appropriately lowered, the focus and tracking control loop becomes unstable and the performance of the disc drive degrades.